Holenesting

Holenesting refers to the behavior of building or occupying nests inside cavities such as tree hollows, crevices, or artificial nesting boxes. This strategy is found across several animal groups but is especially common among birds. In birds, cavity nesting includes species that excavate their own holes (primary cavity nesters) and those that use existing cavities (secondary cavity nesters). Primary nesters include some woodpeckers that create nest holes in dead or decaying wood; secondary nesters include many passerines such as chickadees, tits, bluebirds, and wrens, which rely on holes formed by other animals or by humans.

Nest sites vary from natural tree cavities to old woodpecker holes, rock crevices, and anthropogenic structures like nest boxes, barns, or buildings. Site selection is influenced by factors such as protection from predators and weather, microclimate, hole size and entrance orientation, and competition with conspecifics and other species. Reproductive strategies differ: some species lay multiple eggs per clutch and raise fledglings in a single cavity season, while others reuse cavities across years.

In addition to birds, some insects (notably solitary bees and certain wasps) and a few mammals use holes for nesting or shelter. For insects, cavities in wood or stems provide brood cells and protection from the environment.

Conservation and management emphasize maintaining natural cavities by leaving dead trees and snags when safe, and providing artificial nest cavities to support populations of cavity-nesting species, particularly in forests and urban areas. Competition with invasive cavity-nesting species can pose challenges in some regions.